1. Field of the Invention
The present invention relates to an anti-light-reflective film which is applied to display apparatuses using an EL (electroluminescent) device or liquid crystal device and to photomasks, to a method for manufacturing the film, and to an EL device having an anti-light-reflective function.
2. Description of the Related Art
As an EL device which is used as a display apparatus for office automation or factory automation equipment, there is known an EL device having a three-layer structure as illustrated in FIG. 7. In FIG. 7, transparent strip electrodes 12 made of ITO (indium tin oxide) are patterned on a transparent substrate 10 made of glass so as to be spaced uniformly in parallel to each other. On the strip electrodes 12, a first insulating layer 13 made of an film of oxide such as Al.sub.2 O.sub.3, SiO.sub.2, TiO.sub.2, or of nitride such as Si.sub.3 N.sub.4, a luminescent layer 14 having a composition in which a very little amount of Mn or the like is added as a luminescence center to a host material of ZnS, ZnSe, SrS or the like and a second insulating layer 15 of a similar oxide or nitride film to the first insulating film 13 are laminated in this order, and then back strip electrodes 16 made of Al are patterned in a direction perpendicular to the transparent strip electrodes 12 so as to be spaced uniformly in parallel to each other.
In the thus structured EL device is realized a dot matrix display as desired, by selectively applying a voltage to the transparent electrodes 12 and the back electrodes 16, and then causing portions of the luminescent layer 14 which are at intersections of the transparent electrodes and the back electrodes to emit light in the form of dot in an arbitrary combination.
It is well known in the art that, in front of the aluminum back electrodes 16, i.e. on the side of the second insulating layer 15, an anti-light-reflective film having a laminated structure of a Cr oxide film or a Cr metal film and a laminated structure of a Mo oxide film or a Mo metal film is disposed so as to reduce the reflection of ambient light and improve the contrast ratio of display. For the purpose of absorbing the reflected light, Japanese Unexamined Patent Publication JP-A 61-211997 (1986) discloses utilization of a laminated structure of island-structure type absorbing film/transparent dielectric film/island-structure type absorbing film/metallic thin film by using an island-structure type absorbing film made of Mo, Ta, Cr, Si or the like for a back electrode film.
In the prior art structure in which the back electrodes are made of aluminum as described above, however, since the reflected light from the aluminum back electrodes is rather strong in an bright environment such as the outdoors in the daytime, the contrast ratio (on/off ratio) of display is decreased with the result that the display quality is impaired. In order to solve the problem, JP-A 61-211997 is directed to improvement of the structure of a device so that ambient light (incident light) is absorbed in the device and the intensity of reflected light to the ambient light is controlled to 10% or below.
Although in JP-A 61-211997 is used a Cr metal film for the island-structure absorbing film, the Cr metal film can be replaced with a Cr oxide film. Since in the case of an anti-light-reflective film made of a Cr oxide film or a Cr metal film, toxic dichromatic ion is generated in waste water in an etching process in patterning electrodes, disposal of the waste water in the course of processing cannot be easily conducted. Moreover, since a laminated film including an island-structure type film made of Mo, Ta, Cr, Si or the like requires two or more layers of absorbing film, the laminated film is structured by four or more layers composed of island-structure type absorbing film/transparent dielectric film/island-structure type absorbing film/metal thin film with the result that it takes time to form a laminated film and the cost increases.
An anti-light-reflective film using a Mo oxide film or a Mo metal film in place of a Cr oxide film or a Cr metal film overcomes the above problems occurring by use of a Cr oxide film or a Cr metal film, with regard to the performance, the structure, and the disposal of waste water in a producing process. However, the Mo oxide film and Mo metal film has low water resistance in the manufacturing process, and hence it is difficult to conduct an aqueous-system patterning process. According to experiments by the present inventor, a metallic film is peeled off because the Mo oxide film and Mo metal film is dissolved in a cleaning process by water.
In this way, the prior arts in which a Cr oxide film, a Cr metal film, a Mo oxide film and a Mo metal film are used have drawbacks. In the process of manufacturing a display device, especially an EL device, a structure satisfying all requirements of: being free from a problem of waste water treatment; adaptability to environment; low production cost; and stability in the manufacturing process; has not been realized.